The combination of Yemen's looming civil war, chaos in Somalia, trouble in Saudi Arabia's oil province, increased Israeli and Iranian naval activity in the Red Sea, unrest in revolutionary Egypt have heightened the security threat to the region's maritime chokepoints.

The Bab el-Mandeb Strait, at the southern end of the Red Sea; the Suez Canal at the northern tip; and the Strait of Hormuz, the only way in and out of the Persian Gulf, are all strategic arteries for global oil supplies.

Iran has repeatedly threatened it will close the U-shaped Hormuz waterway, through which one-fifth of the world's oil supplies pass every day, if its nuclear facilities are attacked.

Senior officials in Tehran have warned that "any act of aggression or adventure," including inspection of Iranian vessels' cargoes mandated by the United Nations, would trigger an "appropriate response" and close the strait to international shipping.

The Strait of Hormuz is one of the most vital shipping lanes in the world, carrying oil and natural gas to east and west and any shutdown would reverberate throughout the global economy.

"Maritime chokepoints are among the most sensitive locations where geography, trade and politics meet," a July study by the Institute for National Security Studies at Tel Aviv University stated.

"These points have become increasingly volatile in recent years and especially since the Arab uprisings began" in January, it observed.

"Complications include increased regional instability and aggravation of existing threats, pre-eminently piracy, terrorism and the challenges posed by Iran."

Any closure of the strait by Iran would mean cutting off its own oil exports, its economic lifeline. But opportunities are opening elsewhere.

The Red Sea has become a focus of maritime security concerns, in part because of the pirates plaguing the Gulf of Aden.

The 1,400-mile-long Red Sea is a strategic link between the Mediterranean in the north and the Indian Ocean, where the Bab el-Mandeb -- Arabic for "Gate of Grief" after the navigational hazard it posed ancient mariners -- runs into the Gulf of Aden.

It's been a trading route since 2,500 B.C., the time of the ancient Egyptians who used to maintain commercial links with what is now Somalia, a failed state since 1991 that spawned the current piracy scourge.

Some 3.3 million barrels of Persian Gulf oil pass through the strait every day heading for Suez.

In recent months, the Israeli navy has transited missile corvettes and German-built submarines into the Red Sea from the Mediterranean, while the Iranians sent warships north to Syria, their key Arab ally, via Suez.

It was their first foray into the Mediterranean since the reign of the shah, which ended 32 years ago.

The Israelis have also intercepted what they identified as Iranian arms shipments via the Red Sea to Palestinian militants in the Gaza Strip. Long-range airstrikes in 2010 reportedly took out three such shipments heading through Sudan to Egypt.

That longtime U.S. ally was thrown into turmoil in an 18-day pro-democracy uprising that toppled President Hosni Mubarak in February.

It remains gripped by uncertainty as a military caretaker government ponders reopening links with Iran broken when the shah was overthrown in 1979, while long-suppressed Islamists are widely expected to make major political gains.

In any further upheaval, the Suez Canal, a strategic maritime artery, would be vulnerable.

That was underlined in 2009 when a jihadist cell linked to al-Qaida was broken up while plotting to target ships in the waterway and adjacent oil pipelines.

A year later a group run by the Iranian-backed Hezbollah of Lebanon was smashed plotting to hit similar targets.

Now the Sinai Peninsula, which lies on the canal's east bank, has become insecure as Egypt "is experiencing its greatest political challenge in over half a century," the Israeli INSS report said.

Al-Qaida, eager to target Israel, has apparently moved in and recruited disgruntled Bedouin tribesmen who have attacked a pipeline carrying Egyptian gas to Israel and Jordan at least six times since February.

"It's possible the Suez Canal or the Suez-Mediterranean oil pipeline could become targets for future attacks," INSS said.

U.S. intelligence fears the anarchy in Yemen, which overlooks the Bab el-Mandeb, and Somalia across the Gulf of Aden could merge to threaten the vital sea lanes there already menaced by increasingly sophisticated pirates.